1. Technical Field
The present disclosure relates to a polyimide film and a method for manufacturing the same. More particularly, the present disclosure relates to a polyimide film having inorganic particles and a method for manufacturing the same.
2. Description of Related Art
The polyimide polymer is widely applied due to the excellent mechanical strength, insulating property and high temperature resistance thereof, such as a flexible printed circuit (FPC) applied in various electronic products. A general FPC is formed by etching a flexible copper clad laminate (FCCL) into conducting lines connecting with various circuit components and then covering a layer of polyimide film (Coverlay) thereon with an adhesion agent. The polyimide film is the most important upstream raw material of FPC.
The FCCL can further be divided into two categories: a three-level flexible copper clad laminate (3L FCCL) and a two-level flexible copper clad laminate (2L FCCL). The 3L FCCL is formed by first producing a polyimide film and then pasting the polyimide film to a copper foil through an adhesion agent. The 2L FCCL is formed by directly coating polyimide glue on a copper foil and then molding through baking.
In the FPC, the polyimide film should be combined tightly with the copper foil, and during the process of manufacturing the FPC the polyimide film and the copper foil should be subjected to high-temperature processes such as coating, stretching, laminating, etching and soldering, so that it is important to consider the dimensional variations of the polyimide film and the copper foil after these processes. Due to the above demands, there is a need to create a polyimide film which has a thermal expansion coefficient close to that of a copper foil and high dimensional stability.
In general, manufacturing of the polyimide film can be further subdivided into three steps. Firstly, a polyamic acid solution is obtained by reacting reactive monomers. Subsequently, the polyamic acid solution is applied onto a supporting steel strip or a roller to be shaped as films, and then is stripped after heating and drying to obtain a polyamic acid film. Finally, the polyamic acid film is heated at a high temperature, so that a polyimide film is formed by imidization of the polyamic acid film. This is a continuous scrolling process. During the imidization, due to shrink and strength of the polyamic acid film caused by the high temperature, the physical property of the resulted polyimide film is anisotropic. For example, the thermal expansion coefficient and the mechanical strength of the film layer at a machine direction (MD) is different from that of the film layer at a transverse direction (TD).
In order to solve the problems above, a bi-axial Stretch technique is developed in the industry, such that the film layers at the MD direction and the TD direction have the same thermal expansion coefficient and mechanical strength. However, a production equipment of the bi-axial Stretch technique is expensive and is not convenient to maintain. Furthermore, two sides of the film layer stretched at the TD direction are fixed through a fixture or a pin and the film layer is suspended. However if the film has a large thickness for example larger than or equal to 125 μm, due to the weight of the film and the variation of the film under heat, it is difficult to support the film only through the fixtures or pins at two sides thereof. Therefore, many in the industry are endeavoring to find ways in which to create an improved polyimide film and a method for manufacturing the same, so as to solve the above problems.